Doctrine 2 - How to add custom DBAL driver?

How can I add my custom driver without modifying DriverManager.php in the Doctrine2 core?

I have created a DBAL Driver for pdo_dblib and placed it inside a Symfony2 bundle. This works fine, however I must add my driver to a list of hard-coded drivers in DriverManager.php, otherwise I get the following exception:

Exception

[Doctrine\DBAL\DBALException]                                                                                                                                                   
The given 'driver' pdo_dblib is unknown, Doctrine currently supports only the following drivers: pdo_mysql, pdo_sqlite, pdo_pgsql, pdo_oci, oci8, ibm_db2, pdo_ibm, pdo_sqlsrv

Unless I modify DriverManager.php

final class DriverManager
{
    private static $_driverMap = array(
        'pdo_dblib' => 'Doctrine\DBAL\Driver\PDODblib\Driver', // Added this line
    );
}

Here's my config.yml:

# Doctrine Configuration
doctrine:
    dbal:
        driver:         pdo_dblib
        driver_class:   PDODblibBundle\Doctrine\DBAL\Driver\PDODblib\Driver